Aug. 23, 2010 -- The incidence of rectal cancer increased 3.8% per year between 1984 and 2005 among people 40 and younger, according to a new study. The incidence of colon cancer remained unchanged.

Researchers led by Joshua Meyer, MD, a radiation oncologist at Fox Chase Cancer Center in Philadelphia, used data from the Surveillance, Epidemiology, and End Results (SEER) cancer registry to compare rectal cancer and colon cancer trends. Their findings were released online today and will appear in the Sept. 15 issue of Cancer, a journal of the American Cancer Society.

Colorectal cancer is the second most common cause of cancer-related deaths in the United States, often occurring among older people. Overall, there are nearly 103,000 new cases diagnosed ever year.

Rectal cancer is not considered common among young people, but underestimating the incidence of the disease could lead to missed diagnoses among young people and delayed treatment. According to the American Cancer Society, there are 39,670 new cases of rectal cancer each year; 22,620 in men and 17,050 in women.

Rectal Cancer on the Rise

Meyer and his colleagues looked at data about rectal cancer in patients who were younger than 40 between 1973 and 2005. They calculated the change in incidence over time for colon and rectal cancers. Colon and rectal cancer rates were low overall during the study period, at 1.11 cases and 0.42 cases per 100,000, respectively. However, the incidence of rectal cancer increased among young people -- independently of race or sex -- between 1984 and 2005.

Why rectal cancer is increasing and not colon cancer is not well understood, the authors say. Colonoscopy, a screening tool used to examine the colorectal area for tumors and abnormal growths, may have helped improve the detection of cancer earlier in younger people, they say. However, it is not clear if there are different environmental or genetic factors at play among the younger population.

"We suggest that in young people presenting with rectal bleeding or other common signs of rectal cancer, endoscopic evaluation should be considered in order to rule out a malignancy," Meyer says. "This is in contrast to what is frequently done, which is to attribute these findings to hemorrhoids."

Endoscopic evaluation involves the use of an endoscope, a thin, tubular instrument used for viewing the inside of the body. Increasing endoscopic evaluation among young people with rectal bleeding or other worrisome signs could help reduce delays in diagnosis, Meyer says. The authors do not recommend any changes to current screening guidelines because rectal cancer incidence is still relatively low.